Since the past, an optical module component referred to as an optical receptacle has been used in optical communication using optical fibers. The optical receptacle is configured such that an end portion of an optical fiber held within a cylindrical ferrule is inserted into the optical receptacle together with the ferrule and fixed thereto. In addition, a photoelectric conversion device having a photoelectric conversion element is attached to the optical receptacle. The optical receptacle onto which the photoelectric conversion device and the optical fiber are assembled in this way optically couples the photoelectric conversion element and the end portion of the optical fiber.
Here, FIG. 10 shows an example of this type of optical receptacle 1. The optical receptacle 1 is integrally formed by injection molding of a light-transmitting resin material, such as polyetherimide (PEI), polycarbonate (PC), polyethersulfone (PES), cyclo olefin polymer (COP), or poly(methyl methacrylate) (PMMA).
As shown in FIG. 10, the optical receptacle 1 has a lens 2 in a substantially center position in a length direction. The lens 2 is formed into a plano-convex lens in which a face 2a in one optical axis OA direction of the lens 2 (downward in FIG. 10) is a convex face, and a face 2b in the other direction (upward in FIG. 10) is a planar face.
In addition, as shown in FIG. 10, the optical receptacle 1 has a photoelectric conversion device attaching section 3 that extends from an outer position in a radial direction of the lens 2 towards one optical axis OA direction (downward in FIG. 10). The photoelectric conversion device attaching section 3 is formed into a cylindrical shape of which an inner circumferential surface is a circular cylindrical shape that is concentric with the optical axis OA. However, as shown in FIG. 10, a through-hole 4 is bored into the photoelectric conversion device attaching section 3 to allow gas, generated from an adhesive (such as a thermoset resin) when the photoelectric conversion device is fixed to the photoelectric conversion device attaching section 3 using the adhesive, to escape outside.
Furthermore, as shown in FIG. 10, the optical receptacle 1 has an optical fiber attaching section 5 that extends from the outer position in the radial direction of the lens 2 towards a direction in the optical axis OA direction opposite to the photoelectric conversion device attaching section 3. The optical fiber attaching section 5 is formed into a cylindrical shape of which an inner circumferential surface is a substantially circular cylindrical shape that is concentric with the optical axis OA.
Next, FIG. 11 shows an optical module 7 for reception as an example of an optical module including the optical receptacle 1, such as that described above.
In other words, as shown in FIG. 11, in the optical module 7, a CAN-package-type photoelectric conversion device 8 including an optical reception function is attached to the photoelectric conversion device attaching section 3 of the optical receptacle 1. More specifically, as shown in FIG. 11, the photoelectric conversion device 8 is configured by: a circular disk-shaped stem 9; a light-receiving element 10, such as a photodetector (PD), mounted on the stem 9; a cap 11 having a window portion in a top portion and disposed such as to cover the light-receiving element 10; and a lead 12 through which electrical signals flow based on a light-reception result (photoelectric conversion) of the light-receiving element 10.
In addition, as shown in FIG. 11, in the optical module 7, an optical fiber 15 is detachably attached to the optical fiber attaching section 5 together with a ferrule that holds the optical fiber 15.
In the optical module 7 for reception such as that described above, light including transmission information that has been transmitted from a transmission-side device (such as a semiconductor laser LD) is transmitted over the optical fiber 15 and emitted from an end portion (end face) 15a of the optical fiber 15 towards the lens 2. The light emitted towards the lens 2 is converged by the lens 2 and emitted towards the photoelectric conversion device 8. Thereafter, the light is received by the light-receiving element 10 of the photoelectric conversion device 8. In this way, the end portion 15a of the optical fiber 15 and the light-receiving element 10 are optically coupled.
In the optical module 7 for reception such as that described above, a light-receiving surface of the light-receiving element 10 is formed by silicone or the like. Therefore, as shown in FIG. 12, as a result of the light emitted from the end face 15a of the optical fiber 15 (broken line in FIG. 12) being reflected by the light-receiving surface of the light-receiving element 10, a problem occurs in that the light returns to (enters) the end portion 15a of the optical fiber 15 as optical feedback (double-dotted dashed line in FIG. 12). In particular, in an instance in which a single-mode-type optical fiber 15 is used, such optical feedback may adversely affect the optical output characteristics of the transmission-side device as noise.
To reduce such problems, for example, as shown in FIG. 13, controlling the reflection direction of the light at the light-receiving surface of the light-receiving element 10 to a direction allowing incidence (amount of incident light) of the reflected light onto the end portion 15a of the optical fiber 15 to be suppressed (a direction deliberately shifted from the end portion 15a) by the photoelectric conversion device 8 being attached to the photoelectric conversion device attaching section 3 in a state that is tilted in relation to the optical axis OA of the lens 2 can be considered.
In addition, since the past, various proposals have been made to reduce the problem of optical feedback.
For example, in Patent Literature 1, a proposal is made in which a photoelectric conversion device mounted with a PD chip at an angle is used, thereby suppressing the reflected light from the PD chip from turning into optical feedback.
In addition, in Patent Literature 2, a proposal is made in which the end portion of the optical fiber is attached in a state in which the optical axis of the end portion is tilted in relation to the optical axis of the lens, thereby suppressing the reflected light of the PD from turning into optical feedback after passing through the lens.
Patent Literature 1: Japanese Patent Laid-open Publication No. 2009-258365
Patent Literature 1: Japanese Patent Laid-open Publication No. 2008-83282